Friday, August 12, 2016

Titanosaurian sauropods from the latest Cretaceous of Europe have been documented in the published literature since Matheron (1869) described Hypselosaurus priscus from fragmentary postcranial remains in the Provence region of southern France and Paul Gervais recorded titanosaur remains from marine deposits in the Aquitane region of southwestern France (Buffetaut et al. 1991). Although the discoveries of Ampelosaurus, Atsinganosaurus, Lirainosaurus, Magyarosaurus, Paludititan and now Lohuecotitan (Diaz et al. 2016), attest to the diversity of titanosaurs in the last few million years of the Cretaceous, few authors have attempted to discern the paleobiogeographical origins of Europe's latest Cretaceous titanosaur fauna by cladistic and non-cladistic means (Curry Rogers 2005; Garcia et al. 2010). However, the description of the aralosaurin lambeosaurine hadrosaurid Canardia from the same region as Ampelosaurus and Atsinganosaurus (Prieto-Marquez et al. 2013), the recognition of Pararhabdodon as a relative of the tsintaosaurin lambeosaurine Tsintaosaurus by Prieto-Marquez and Wagner (2009), and the discovery indeterminate titanosaur remains from the Bissekty Formation of Uzbekistan and the Dabrazinskaya Svita of Kazakhstan (Riabinin 1939; Sues et al. 2015), has led me to consider the possibility that either all titanosaur species from latest Cretaceous Europe, or at least some taxa, were descended from a titanosaur that immigrated to Europe from Central Asia during the latest Cretaceous.In their description of titanosaur remains from the Bissekty Formation, Sues et al. (2015) note that the titanosaur braincase CCGME 628/12457 differs from the braincases of Lirainosaurus in lacking distal foramina on the basal tubera of the paroccipital processes and basal tubera separated by a wide depression ventral to the occipital condyle, with a round pit forming the center of the depression. Nevertheless, the presence of the abducens nerve VI extending lateral to the pituitary fossa is shared by both Lirainosaurus and CCGME 628/12457 along with other derived titanosaurs (cf. Sues et al. 2015, figs. 3-4 with Knoll et al. 2013), and the fact that the aforementioned features of the Bissekty braincase are also seen in several titanosaurs for which braincases are known (e.g. Jainosaurus, Muyelensaurus, Nemegtosaurus, Pitekunisaurus, and Rapetosaurus) may dampen the usefulness of braincase characters for determining the biogeographical origins of late Cretaceous European titanosaurs.Although Garcia et al. (2010) suggested that Atsinganosaurus could be a European descendant of African lithostrotians based on comparisons with the caudal vertebrae of the basal lithostrotian Malawisaurus, they caution that a comprehensive phylogenetic analysis of Titanosauria is needed to confirm or refute the possibility of a Gondwanan origin for Atsinganosaurus. As a matter of fact, the near-lack of sauropod remains from pre-Turonian Cretaceous sediments in Central Asia (see Weishampel et al. 2004 for available records) suggests that a group of lithostrotians more primitive than Saltasauridae may have colonized Central Asia from Gondwana via rudimentary land bridges to Asia, because Garcia et al. (2010) note that Ampelosaurus and Lirainosaurus are more derived than Atsinganosaurus. Likewise, the placement of Ampelosaurus, Lirainosaurus, and Lohuecotitan by Diaz et al. (2013, 2016) and Garcia et al. (2013) bolsters the alternative hypothesis that even if some European titanosaurs are more primitive than others, they still could have evolved from a Central Asian ancestor because of the dearth of Early Cretaceous (Neocomian) non-avian dinosaur fossils from Central Asia.